Developments in tennis racket frames have been pronounced in recent years and various frames, string supports and handle structures have been proposed utilizing frame members composed of various materials and fabricated by various methods.
In spite of the considerable efforts which have been exerted to develop the perfect tennis racket, improvements are constantly being made and, indeed, are constantly being sought.
It is important for a tennis racket frame to have high stability, light weight and freedom from the tendency to generate disconcerting sounds. Other desiderata for effective tennis racket frames include long useful life, resistance to breakage, ease of assembly, etc.
In recent years the desire for high-strength low-weight rackets has resulted in the development of tennis racket frames which are composed of metal, metal-reinforced plastic or even esoteric composites (e.g. carbon, glass or other fiber reinforced synthetic resin), tubular or hollow-profile frames.
Where the opposite sides of the frame are brought together to be incorporated into the handle, a bridge or heart piece of tubular material is spanned across the bottom of the oval to complete the enclosed area which is to be spanned by the strings.
The heart or bridge piece also increases the stability of the frame against twisting. It is generally located in the region at which the frame sides are bent from their oval-forming curvature to the handle-forming curvature.
It has been a common practice to connect this bridge piece to the opposite sides of the tubular frame by rivets. With use of the racket, however, the rivets, their heads and the regions adjacent the rivets were highly stressed and the rivet connection tends to loosen. With even the slightest loosening, the racket began to produce unpleasant sounds when the ball was struck as a result of the friction of the bridge piece and the remainder of the frame or friction in direction between the rivet and the members joined by it. It was not uncommon for the rivet to break with time.
In another approach the heart piece or bridge was welded to the frame members. This, however, resulted in stresses in the material of the frame or the bridge piece leading to breakage of the frame.